Side wall and bottom wall discharge bins of the type shown in U.S. Pat. Nos. 2,648,428 and 3,104,035 and slope bottom bins of the type shown in U.S. Pat. No. 3,329,317, have been used extensively for storing and transporting bulk material. The principal problem that has been encountered with the side and bottom wall discharge bins is that it has been necessary to provide a door over a discharge opening on the side or bottom of the bin. In normal handling of the bin during transport and storage, these doors experience considerable banging around and general rough useage by fork lift operators and others. This makes it difficult to maintain a dust tight seal between the door and the bin due to the extensive abuse of the door. Also, many of the prior art bins of the side wall and bottom wall discharge type have required special equipment for discharging the bin contents. Rapid discharge of the slope bottom bin shown in the above patent is impossible because it has a discharge opening of very small size. It is an object of the present invention, therefore, to provide an improved self-emptying bin with an internal discharge opening and door arrangement that is protected from rough handling and thereby insures an improved door seal over a prolonged service life of the bin.